4210 jig & 1/2 box joints

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Forum topic by SRHD posted 04-10-2011 09:32 PM 1734 views 0 times favorited 6 replies Add to Favorites Watch
View SRHD's profile


4 posts in 2572 days

04-10-2011 09:32 PM

Hello everyone,
My first post on the boards but I have been coming here and reading different reviews and posts about stuff for over a year. I figure its about time i join the forums lol.

I have a problem and I think i know the solution but I don’t want to waste any more on a new bit that may not work.

I have the porter cable 4210 jig and I am using the 1/2 box joint jig i bought for it.
It says to hold it against the left guide as you cut the fingers to avoid loose joints and I am doing that but they are still far too loose for my liking. There is almost no resistance as you put the pieces together.
The Fingers are cutting at between .485 to .490
The spaces are between .506 and .508.
I know the bit is exactly at .500

This creates a space about .018 to .020

So I figured since 1/64 is .015 changing the bit to a 31/64 would get me within .003 and .005 over and they would be tight

So I think because I am not a CNC machine, or lack of years of practice and since I don’t have unlimited board feet to practice with; maybe compensate for that with a undersized bit, like the 31/64th (undersized 1/2).

I normally make my boxes out of walnut, pine, oak or maple .

Do you guys think that would work or would they be too tight and I would end up having to sand the crap out of them to fit. My thinking is tighter is better because then I could always remove a little but I don’t want to be there all day on a joint…would the wood compress and give me the space I need or do you think I would be asking too much from a hardwood..

Am I overlooking something? I don’t like wasting money so I figured I would run it by all your brains.

6 replies so far

View ajosephg's profile


1880 posts in 3530 days

#1 posted 04-10-2011 11:19 PM

I would postulate that your guide bushing is not exactly centered in your router plate. I had the same problem making 1/4 inch box joints with my PC jig.

If that’s the case you have two options
1. Drift the holes in the plate to center (easier said than done)
2. When cutting, make sure you hold the router in the same “clock” position at all times in addition to holding it to the left side of the template.

-- Joe

View Gerry's profile


264 posts in 3209 days

#2 posted 04-10-2011 11:35 PM

Welcome to Lumberjocks! I wish I had the experience to help, but i wanted to welcome you, and assure you there are so many great, helpful folks here, that I’m sure my lack of info won’t be an impediment. Good Luck!

-- -Gerry, Hereford, AZ ” A really good woodworker knows how the hide his / her mistakes.”

View SRHD's profile


4 posts in 2572 days

#3 posted 04-11-2011 12:20 AM

Hello . thanks for the welcome gerry and advise joe.

I definitely have it clocked the same. Im going to try again pushing harder to the left and recenter the base too. It looks right but with such small tolerances it would be hard to eye the difference.

Thanks again

View ajosephg's profile


1880 posts in 3530 days

#4 posted 04-11-2011 02:31 AM

I use the alignment cone that comes with the guide bushing set (from Rockler) to check the base alignment. I had to modify the base by counter boring the mounting holes. Don’t understand why Porter Cable would put tapered holes. Maybe someday I’ll buy an after market base that is more accurate, because I haven’t been able to get the centering better than about 0.005.

In a way though it has a good side effect. For example if the joints are too tight you can rout them with the router handles at say 3:00, and then turn them to 3:15 and route again, and voila, the width is slightly increased. Maximum adjustment would result if the clock was adjust to 3:45 (I think).

Good luck

-- Joe

View drewnahant's profile


222 posts in 3057 days

#5 posted 04-11-2011 02:39 AM

Maybe somebody else can tell you if this idea has any value, but I would check that your router bit is a true .500, and perfectly balanced. If it is larger, or if it is off center, it will be impossible to get the exact .500 cut that you need. Maybe you just need a better quality bit.

View SRHD's profile


4 posts in 2572 days

#6 posted 04-11-2011 06:18 AM

I have an alignment thing for my bosch too and it works well, I need to double check the centering but Im pretty sure its as close as I am going to get it.

The bit is .500 for sure, double checked. I never got back to it today so going to give it a whirl tomorrow just by checking center and pressing harder to the left. It may have been drifting and I didn’t notice.

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